The present invention relates to a semiconductor device, more particularly, to a semiconductor device with a multipurpose pad.
Considering a fabrication process for semiconductor devices, first, many semiconductor dies are created on a single wafer. Typically, several dozens or hundreds of semiconductor dies are produced on a wafer. After fabricating semiconductor dies, wafer level tests are executed to check fabricated semiconductor dies on the wafer for errors. Semiconductor dies which pass wafer level testing are sawed and packaged in plastic cases. A packaged semiconductor die is called a semiconductor device.
As demand for reducing fabrication costs for semiconductor devices grows, semiconductor manufacturers are attempting to reduce the size of semiconductor dies. As the size of semiconductor dies on a wafer decreases, the number of semiconductor dies included on the wafer increases. The more dies included in a wafer, the lower the cost for the end semiconductor device. Therefore, semiconductor dies have become smaller and smaller. In the other hand, packages for the semiconductor dies have to have a predetermined size because the package size of a semiconductor device is fitted with the size of its predetermined place on a printed circuit board (PCB), which includes the semiconductor die. In particular, the width or gap of signal lines arranged on the PCB should be matched with that of pins connected to the package of the semiconductor die.
Generally, a semiconductor die includes a plurality of pads corresponding to the package pins for the semiconductor die. The pads included in the semiconductor die are respectively coupled to input signals into and output signals from logic circuits created in the semiconductor die. Thus, through pads included in the semiconductor die, signal lines for logic circuits created in the semiconductor die are connected to signal lines arranged on a PCB.
The pads of the semiconductor die are conductive patterns arranged on space remaining between the logic circuits. The magnitudes of signals on signal lines of the logic circuits in the semiconductor die are too small compared with the load capacitances of signal lines on a PCB. Thus, the magnitudes of signals on signal lines of the logic circuits should be raised through signal output drivers to output signals and also the pads of the semiconductor die has sufficient load capacitances to correspond to load capacitances of signal lines on the PCB. Hence, the pads of the semiconductor die should occupy a relatively large area of the semiconductor die.
Typically, pads for semiconductor dies are classified into input pads for receiving signals from external signal lines, output pads for outputting signals from the logic circuits to external signal lines, power pads for supplying external power and test pads for transferring test signals during testing.
As semiconductor technology develops, the demand for carrying out more complex operations and reducing power consumption of semiconductor devices increases. Also, the number of input pads and output pads for a semiconductor device increases and the level of a power supply voltage supplied to a semiconductor device decreases more and more. As a result, the number of pads needed for receiving power signals increases. Because power signals through the power pads of a semiconductor device become more susceptible to external noises as a power supply voltage supplied to a semiconductor device decreases, the semiconductor device should include many more pads for receiving power signals. In the situation that the number of pads to be included in a semiconductor die is limited, a semiconductor device does not have a sufficient number of test pads for testing. That is, the number of test pads of a semiconductor device should be strictly limited.
When all of the pads in a semiconductor device are assigned depending on use, at first, input pads or output pads are arranged and pads for power signals are assigned. And then, the remaining pads can be assigned as test pads. The number of remaining pads assigned for the test pads is often insufficient for executing various tests.
Because the desired tests of a semiconductor device have become various and complex as semiconductor technology has developed, there is a need for an increasing number of test pads for testing a semiconductor device. However, described above, the number of available test pads has decreased. That is, because of the lack of the desired number of test pads, sufficient test signals corresponding to various tests can not be supplied to a semiconductor device under test and semiconductor manufacturers can not check test results in response to supplied test signals. If a fabricated semiconductor device has an error, it can not be thoroughly checked so as to find the error because the required number of test pads is lacking and as a result, the necessary test signals can not be supplied to a fabricated semiconductor device.